Due to the considerable loads that a tower of a wind turbine experiences during its lifetime, the tower needs to be firmly attached to the foundation of the wind turbine. This connection between the tower and the foundation is typically realized by a plurality of bolts. A flange is often situated on top of the foundation. The bolt connection then connects this flange with the bottom end of the tower.
Conventionally, the bottom end of the tower also comprises a flange, which corresponds to the flange which is present on the foundation. The foundation may be made of concrete and the flange which connects the foundation with the bottom end of the tower is placed in liquid concrete. In other words, the concrete has not yet solidified.
In the case that the flange connects the bottom end of the tower via bolts these bolts are typically arranged such that the bolt head is at the bottom, i.e. facing the foundation. After solidification of the concrete, a nut or a similar fastening element tightens the bolt at the side which is facing the bottom end of the tower.
In the described approach of connecting the tower with the foundation, the bolt head is surrounded by liquid concrete during a certain time period. This leads to the problem that concrete or grout could enter into the space between the bolt head and the flange.
This problem has been addressed in the international patent application WO 2011/047723 A1. Therein, it is proposed to provide a disc or cover to a nut cage, wherein the nut cage surrounds the nut which is at the bottom side of the flange. Such a covered nut cage claims to be able to reduce the risk for grout or concrete entering the space between the bolt head and the base flange.
This solution, however, has the drawback that it requires a relatively complex and costly provision of a covered nut cage.
Therefore, there exists the desire to provide a more simple and inexpensive way of reducing the risk that impurities such as grout or concrete enters the space between a bolt head and a flange of a bolt connection.